This invention relates in general to an apparatus for applying refractory material and more particularly to a gun capable of mixing dry refractory material with water and then discharging it with substantial force against a wall.
The heating and other operations carried on within furnaces lined with refractory material eventually erode or burn away portions of the refractory material. The refractory material requires replacement in order to restore the furnace to a useful condition. If the furnace is cooled to allow a repairman to enter the furnace safely, valuable production time is lost.
One method of repairing refractory linings of furnaces, boilers, and the like, without cooling the equipment and thereby losing substantial production time, is to pneumatically apply granular refractory mixtures to the hot furnace walls by means of a cement gun. The granular refractory mixture is blown by compressed air from a supply apparatus through hoses to a gun which is held by the operator such that the tip of its discharge nozzle is about 18 inches to 24 inches from the deteriorated lining which is to be repaired. Water is injected into the refractory mixture before it enters the discharge nozzle to enhance the bonding or "sticking" qualities of the mixture and to cause cement in the mixture to set.
Some furnaces are too large for the operator to bring the discharge nozzle to the prescribed distance from the lining for gunning and in such instances a pipe extension of the desired length is commonly inserted in the gun between the point of water injection, and the discharge nozzle. These extensions cause a loss of velocity and when the gun is inserted into a hot furnace, the pipe extension is heated, thus causing the moistened refractory material to stick to the inside of the pipe, clogging the same. To alleviate this problem, various devices have been tried which move the point of water injection or ring away from the operator and closer to the nozzle.
U.S. Pat. No. 2,419,410 shows a nozzle extension that is cooled by a water spray from holes in a pipe running parallel to the extension. A water ring also is used to wet the refractory material before it enters the nozzle.
To wet the refractory material, it has been a common practice to inject water into the material supply pipe within the gun before the material reaches the discharge nozzle. Devices heretofore developed for water injection cause uneven and ineffective distribution of the moisture through the material. This in turn results in a poor bond with the existing lining, and the newly applied refractory material tends to "rebound" from the existing lining. The material must be thoroughly wetted to achieve low rebound losses.